أَلَمْ نَجْعَلِ ٱلْأَرْضَ مِهَـٰدًا
Sentence structure
The rhetorical question draws attention to Allah's power. نَجْعَلِ has an understood subject نَحْنُ, ٱلْأَرْضَ is its first object, and مِهَـٰدًا is its second object.
أَلَمْ — Did We not?
Grammar: The prefixed أَ is interrogative. لَمْ negates past meaning and makes the following imperfect verb jussive.
نَجْعَلِ — We made / appointed
Grammar: A first-person plural imperfect verb made jussive by لَمْ, with understood subject نَحْنُ. The final kasrah is a joining vowel before hamzat al-waṣl, not the mood marker.
ٱلْأَرْضَ — the earth
Grammar: A definite feminine accusative noun and the first object of نَجْعَلِ.
مِهَـٰدًۭا — a resting place / spread
Grammar: An indefinite masculine accusative noun and the second object of نَجْعَلِ.